Hiroshi is a boy who is somewhat lazy in school and his daily tasks. One day, while fighting against his bullying classmates, Hiroshi accidentally falls on a frog that was hopping through Nerima, Tokyo's Shakujii Park. As a result of this incident, Pyonkichi, the frog, becomes a 'flat frog,' and his image and spirit become imprinted on Hiroshi's t-shirt. Since this shirt is the only one Hiroshi has kept in good condition, he is forced to wear it every day, interacting with Pyonkichi and forming a friendship. Pyonkichi has complete control over the t-shirt, able to move it at will, regardless of Hiroshi's wishes.
